Antireflective polymer films (“AR films”), or AR coatings, are becoming increasingly important in the display industry. New applications are being developed for low reflective films and other AR coatings applied to articles used in the computer, television, appliance, mobile phone, aerospace and automotive industries.
AR films are typically constructed by alternating high and low refractive index polymer layers in order to minimize the amount of light that is reflected. Desirable features in AR films for use on the substrate of the articles are the combination of a low percentage of reflected light (e.g. 1.5% or lower) and durability to scratches and abrasions. These features are obtained in AR constructions by maximizing the delta RI between the polymer layers while maintaining strong adhesion between the polymer layers.
It is well known that the low refractive index polymer layers used in AR films are usually derived from fluorine containing polymers (“fluoropolymers” or “fluorinated polymers”), which have refractive indices that range from about 1.3 to 1.4. Fluoropolymers provide unique advantages over conventional hydrocarbon based materials in terms of high chemical inertness (in terms of acid and base resistance), dirt and stain resistance (due to low surface energy), low moisture absorption, and resistance to weather and solar conditions.
The refractive index of fluorinated polymer coating layers is dependent upon the volume percentage of fluorine contained within the layers. Increased fluorine content decreases the refractive index of the coating layers.
However, increasing the fluorine content also decreases the surface energy of the coating layers, which in turn reduces the interfacial adhesion of the fluoropolymer layer to the other polymer or substrate layers to which the layer is coupled.
Other materials investigated for use in low refractive index layers are silicone-containing polymeric materials. Silicone-containing polymeric materials have generally low refractive indices. Further, silicone-containing polymeric coating layers generally have higher surface energies than fluoropolymer-base layers, thus allowing the silicone-containing polymeric layer to more easily adhere to other layers, such as high refractive index layers, or substrates. This added adhesion improves scratch resistance in multilayer antireflection coatings. However, silicone-containing polymeric materials have a higher refractive index as compared with fluorine containing materials. Further, silicone-containing polymeric materials have a lower viscosity that leads to defects in ultra-thin coatings (less than about 100 nanometers).
Thus, it is highly desirable to form a low refractive index layer for an antireflection film having increased fluorine content, and hence lower refractive index, while improving interfacial adhesion to accompanying layers or substrates.